Hitherto fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether has been extensively utilized as an inhalation anesthetic which is safe for use. A method of producing fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether is described in detail in U.S. Pat. No. 4,250,334, and arranged as follows: First, concentric sulfuric acid and hydrogen fluoride are added to paraformaldehyde to obtain a reaction mixture. Then, 1,1,1,3,3,3-hexafluoroisopropyl alcohol is added dropwise to the reaction mixture upon being heated, thereby to generate gas which is to be collected. The collected gas contains unreacted 1,1,1,3,3,3-hexafluoroisopropyl alcohol, and by-products such as formal, acetal and the like, in addition to the objective product of fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether.
Besides, International Publication No. WO97/25303 describes a method of producing fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether, arranged such that bis(fluoromethyl)ether, 1,1,1,3,3,3-hexafluoroisopropyl alcohol and sulfuric acid are mixed with each other thereby to obtain fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether together with unreacted bis(fluoromethyl)ether and acetal.
Regarding the above production methods of fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl alcohol has the generally same boiling point (about 58.6° C.) as that of the objective product (fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether), and therefore it seems that the recovered objective product contains 1,1,1,3,3,3-hexafluoroisopropyl alcohol though the content of 1,1,1,3,3,3-hexafluoroisopropyl alcohol is different in accordance with reaction conditions.
In regard to the above, it is impossible to separate 1,1,1,3,3,3-hexafluoroisopropyl alcohol from fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether under distillation which is the most commonly used for purification of organic substances, since they have the generally same boiling points. Additionally, separation of them is impossible even under a separation method employing the difference in freezing point (−68° C. and −3.3° C.) between them. Additionally, even though 1,1,1,3,3,3-hexafluoroisopropyl alcohol is soluble in water in any mixing ratios between them, it cannot be sufficiently removed upon rinsing with water.